More than half a million patients in the US and Western Europe whose kidneys are failing and need to undergo hemodialysis face a significant risk. This risk is due to the limitations and performance issues of current methods for a dialysis machine to connect to a patient's circulatory system known as a vascular access (VA) site. Achieving long-term vascular access which remains patent and infection free is very difficult. (See Leermakers et al. (2013); US Dept. Health and Human Services Report (2014); and Al-Jaishi et al. (2014)).
Vascular access can be achieved in one of three ways: arteriovenous prosthetic grafts (AVG), tunneled central vein catheter, or native arteriovenous fistula (AVF). The main function of both the AVF and the AVG is to create a “short circuit” in the peripheral vasculature by directly connecting high-pressure arterial flow and low-pressure venous flow. This results in a greatly increased flow rate, which is necessary for dialysis, in the graft or the vein. The latter also enlarges and arterializes making it easier to cannulate.
Currently a patient requires open surgery with local or general anesthesia to receive an AVF. Once the AVF has been created one needs to wait until it matures and is ready to be used for hemodialysis (HD). VA's can fail due to a variety of reasons including thrombosis, stenosis, infection, or neointimal hyperplasia. Overall, there is a need for a VA which is easy to implant, matures quickly and has a high patency rate.
Minimally invasive surgery is a common method to perform a variety of cardiovascular procedures. It is typically performed using catheters that are inserted into various lumens within the body through small incisions in the skin. A percutaneous approach to AVF creation has several clinical benefits including simplifying the procedure and reducing surgical trauma to the vessels which has a negative effect on patency.
Several technologies have been developed with the purpose of creating an arteriovenous fistula percutaneously however none have been approved for clinical use. All of the following technologies employ one or two catheters in order to create an anastomosis between two adjoining blood vessels. U.S. Pat. No. 8,523,800 describes technology for forming a fistula with the aim of treating COPD patients and those with hypertension. U.S. Pat. No. 5,830,222 and WO2006/027599 describe technology for percutaneously connecting two vessels to divert arterial blood to the venous system, and U.S. Pat. No. 6,475,226 describes an alternative to coronary bypass surgery. US2013/0281998 and US2012/0302935 describe technologies for percutaneously creating fistulas for dialysis use.
There are several suitable anatomical locations for the vascular anastomosis which allow for the formation of a vascular access site suitable for haemodialysis. The most commonly used include in the radial artery and cephalic vein at the wrist level, the brachial artery and cephalic vein at the antecubital fossa, and the brachial artery and basilic vein in the upper arm. Less commonly a fistula can be created in the upper leg between the saphenous vein and femoral artery.
There are two main approaches to using intravascular catheters for creating the anastomosis; one technique involves placing a tube or stent graft between the two vessels in order to form the connection, the other creates a hole directly between the two vessels where they are close together. Implementing either technique requires an active means to align the two catheters, as fluoroscopy is not adequate for the angular alignment. Accurate alignment is more important in the first case when the ratio of the vessel separation to the vessel diameters increases.
Several different modalities for radial alignment have been presented in the literature and typically include a transmit catheter sending a signal toward a receive catheter which measures the magnitude of the signal and relays that information as an indication of alignment. Different types of signals include ultrasound (see, for example, WO2006/027599, US2004/0133225), light (see, for example, U.S. Pat. No. 6,475,226), and inductive fields (see, for example, EP1377335). However, a drawback of such methods is that they require relatively complex mechanical or electronic transducers, to generate and receive the signals, which can be difficult and expensive to manufacture and limit the size of the catheters, in particular their suitability for use in smaller diameter vessels.